Although perhaps a little late for Halloween, last year I found a website that specialises in making papier mache sculptures. Some look quite complex, but they give detailled instructions on how to make each design. Have a look on the right hand side of the home page, under ‘Pages’ and click on a link that takes your fancy.
There is also a ‘Basics‘ section where he tells you how to make the special papier mache paste. I urge you to look at this section before you give it a go! I made a pumpkin last year so I’ll try and find a picture for you and put it up here.